Vacuum indicating buttons on closures are used extensively for the food industry because they are an effective quick-detection means and lets one know some very important conditions about the associated container. For example: Is the container sealed?--is the button in the "down" position; has the container been opened, or tampered? If the button is in its "up" position; has the seal been broken because of other causes, such as: severe handling, slow leakage or cracked glass of the container at the seal area that could result in product spoilage?
It is also very reassuring to hear the button "pop" as the closure is twisted off the container. In addition, the button is an invaluable quality control means at the product filling operation. With automatic type detection equipment, the button lets the packer know, instantly, whether to accept the sealed container (button "down") or reject it (button "up") because a seal was not attained.